Walk in bathtubs are generally equipped with an outlet or drain to facilitate high-flow drainage such that the contents of the bathtub can be emptied as quick as possible to avoid the user remaining in the bathtub for an unnecessary period of time.
A walk in bathtub typically includes an access door for ease of entry and exit, which eliminates the need for a user to straddle the edge of the bathtub to step into or out of the bathtub. Upon entering the bathtub, the access door closes and seals relative to the side of the bathtub such that the bathtub can be filled with water.
Typically, the bathtub needs to be emptied, almost fully, before the door can be opened to avoid water spilling onto the bathroom floor.
Modern bathtubs and sanitary-ware generally include substantially integral plug units which involve closing the outlet/drain from the bath by mechanical means. For example, a pop-up plug, which remains in contact with the outlet at all times. This type of plug changes position or orientation relative to the outlet to close and open the outlet.
In the situation of a high-flow drain these types of plug inserts have the problem that as water exits the bath, the volume of water is capable of generating sufficient force to cause the plug unit to engage with the outlet and therefore halt the draining process. It will be appreciated, in the context of a walk-in bath, this situation is not desirable because the user generally needs to remain in the bath until all or most of the water has drained away.